Optical recording process

ABSTRACT

An optical recording medium comprising a substrate having a pre-groove for focusing and tracking servo operation, and a recording film formed on the substrate, the recording film having optical properties which change in response to the application of at least one of a light beam or heat to a portion of the recording film.

This is a division of application Ser. No. 07/545,941, filed Jun. 29,1990, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to an optical recording process whichprovides on a substrate a recording film having such optical propertiesas are variable by means of light, heat, and so forth and performs therecording, reproduction, and erasure of information through itsutilization of changes in the said optical properties and moreparticularly to improvements an such an optical recording process sothat it is capable of maintaining the recorded information over a longperiod of time.

The principal parts of the optical recording medium used for this typeof optical recording process are comprised, for example, of (a) apre-groove for use in focusing and in tracking servo operation as shownin FIG. 49, (b) a light-transmissive substrate in which the saidpre-groove (a) is formed, (c) a recording film formed uniformly over thesurface of this substrate (b), and (d) a protective film formeduniformly over the surface of this recording film (c), and the opticalrecording process perform the reproduction of the information recordedon the said medium by irradiating the convergent beam of light (f) fromthe light source, such as a semiconductor laser unit, onto the recordingfilm (c) of this optical recording medium and having the reflected lightthereof input into a light-receiving element (not illustrated in theFigure), such as a photodiode.

In this regard, the conventional optical recording process is availablein two types, namely, the recording and reproducing type of the process,which is not capable of performing the rewriting of the recordedinformation, and the recording, reproducing and erasing type of theprocess, which is capable of performing the rewriting of the recordedinformation, and the known processes of the former type, i.e. therecording and reproducing type, are the "ablative process" and the"bubble process".

The "ablative process" is a process whereby a laser beam or the like isirradiated onto the surface of the recording film (c) on the opticalrecording medium mentioned above, as shown in FIG. 50, so that therecording film (c) in the irradiated area is thereby caused to have adissolution resulting in the exposure of the surface of the substrate(b). Thus, this process performs the recording and reproduction ofinformation through its utilization of the difference between thereflection factor of the opened area (g) and that of the unopened area.On the other hand, the "bubble process" is a process which irradiates alaser beam, as shown in FIG. 51, and heats some part of the substrate(b), thereby forming bubbles (h) in the irradiated area by using thepressure of the gas generated from the substrate (b). Thus, this processperforms the recording and reproduction of information throughutilization of the difference between the reflection factor of the areawhere the bubbles are formed and that of the area where such bubbles arenot formed.

On the other hand, the process of the latter type, namely, therecording, reproducing and erasing type, which is capable of rewritingthe recorded information, is a process which reversibly changes theoptical properties of the above-mentioned recording film (c) by suchmeans as light and heat, as shown in FIG. 52, and performs therecording, reproduction, and erasure of information through itsutilization of the said changes in the optical properties of therecording film. The known processes realized in concrete form are the"phase changing process" and the "magneto-optical process".

In specific terms, the "phase changing process" consists of irradiatinga high output laser spot onto a part of the recording film (c) in thecrystalline state (cr) as shown in FIG. 53 and thereby transforming theirradiated area from its crystalline state (cr) into its amorphous state(am) through the application of a high speed high temperature heatingtreatment and a high speed quenching treatment to the irradiated area,and performing the recording and reproduction of information through theutilization of the difference in the reflection factor between the areain the crystalline state (cr) and the area in the amorphous state (am)(See FIG. 54). In the meanwhile, this process performs the erasure ofrecorded information by irradiating a laser spot beam at a low outputonto the recorded area of the recording film (c) mentioned above, asshown in FIG. 55, thus applying a heating treatment at a low temperatureand a cooling treatment at a relatively slow pace, thereby transformingthe irradiated area from its amorphous state (am) into its crystallinestate (cr), i.e. the state of the recording film prior to recording.

On the other hand, the "magneto-optical process" irradiates a laser spotbeam onto the recording film (c) composed of magnetic material while itis in the state where a magnetic field is applied in the directionindicated by the arrow mark, as shown in FIG. 56, and, using a change inthe Kerr rotating angle (Refer to FIG. 57) as effected by changing thesaid angle by reversing the direction of magnetization in the irradiatedarea, this process performs the recording and reproduction ofinformation. This process performs the erasure of recorded informationby irradiating a laser spot beam to a recorded area of the recordingfilm (c) in the state where the direction of the magnetic field isreversed from that at work at the time of recording, as shown in FIG.58, thereby putting the direction of magnetization in the irradiatedarea back to the state of the area prior to recording.

However, these existing optical recording processes present suchproblems as those mentioned below.

First, the "ablative process" and the "bubble process" of the recordingand reproducing type have the problem that the shapes of the openingsand those of the bubbles formed on the recording film, as well as therecording film itself, are susceptible to change over the passage oftime, thus lacking stability for the maintenance of recordedinformation. In addition, it is not possible for the processes torewrite the recorded information.

On the other hand, the "phase changing process" of the recording,reproducing, and erasing type has the problem that it lacks stabilityfor the maintenance of the recorded information, as is the case of the"ablative process" mentioned above, since the amorphous region, which isin a semi-stable state, tends to be crystallized over the passage oftime because the crystalline region and the amorphous region, which aredifferent from each other in terms of their energy levels, are presentside by side on the recording film after the completion of recording ofinformation thereon by the process which, as described above, performsthe recording, reproduction, and erasure of information through itsutilization of the changes in optical properties attending the phasechange between the crystalline state and the amorphous state.

Moreover, the "magneto-optical process" of the recording, reproducing,and erasing type, which is a process for reproducing the recordedinformation by detection of the Kerr rotating angle as described above,also harbors the problem that it lacks stability for the maintenance ofrecorded signals because such readily oxidized materials as Tb and Fecontained in the recording film are oxidized along with the passage oftime.

SUMMARY OF INVENTION

In view of the above problems of the prior art, it is an object of thisinvention to provide an optical recording process which is capable ofmaintaining recorded information over a long period of time.

According to the present invention, an optical recording processprovides on a substrate a recording film having such optical propertiesas are variable by means of light, heat, and so forth and performs therecording and reproduction of information or the recording,reproduction, and erasure of information through its utilization ofchanges in the optical properties.

Thus, the optical recording process is characterized by achieving aselective phase separation of the recording film by such means as lightand heat, thereby changing the optical properties in the region of thefilm.

In particular, the recording process of the present invention ischaracterized by the formation of the above-mentioned recording filmwith recording material wherein the miscibility gap line appears in theliquid phase region as observed in the phase diagram and also byrewriting the information by means of one beam, which is a singlerecord-erasing beam yielding selectively variable output onto thesurface of the recording film mentioned above.

Moreover, the recording process of the present invention ischaracterized by providing a heat interfering layer having heatradiating effect in the area adjacent to the recording film mentionedabove and by causing the occurrence of a phase separation attending aspinodal decomposition by applying a high temperature heating treatmentand a quenching treatment to the recording film.

BRIEF DESCRIPTION OF THE DRAWINGS

The manner by which the above objects and other objects, features andadvantages of the present invention are attained will be fully evidentfrom the following detailed description when it is considered in lightof the accompanying drawings, wherein:

FIG. 1 through FIG. 5 illustrate the examples of preferred embodimentsof the present invention;

FIG. 1 is a schematic sectional view of the optical recording mediumused in the first example of preferred embodiments of the presentinvention;

FIG. 2 is a quasi binary phase diagram for the material whichconstitutes the recording film;

FIG. 3 through FIG. 5 respectively illustrate approximate sectionalviews of the optical recording media used in the second through fourthexamples of preferred embodiments of the present invention;

FIG. 6 and FIG. 7 illustrate the binodal decomposition and the spinodaldecomposition;

FIG. 6 is a graph showing the relationship between the free energydifference (ΔG) and the molar fraction (χ) in the binary alloy systemcomposed of A and B.

FIG. 7 is a graph showing the binodal decomposition region and thespinodal decomposition region;

FIG. 8 is an enlarged chart illustrating the structure of the regionwhere the phase separation has occurred along with the binodaldecomposition;

FIG. 9 is an enlarged chart illustrating the structure of the regionwhere the phase separation has occurred along with the spinodaldecomposition;

FIG. 10 through FIG. 48 respectively present the quasi binary phasediagrams for the materials which can be used for the recording film asdefined herein for the present invention;

FIG. 49 is partial perspective view of the optical recording medium usedfor the conventional optical recording process;

FIG. 50 through FIG. 52 are partial enlarged views of what is shown inFIG. 49;

FIG. 53 through FIG. 55 illustrate the principles of recording,reproduction, and erasure by the "phase change process"; and

FIG. 56 through FIG. 58 illustrate the principles of recording,reproduction, and erasure by the "magneto-optical process".

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term, "phase separation", as used hereinabove is a thermodynamicallyexplainable characteristic phenomenon which occurs in common to a groupof materials composed of a plurality of constituents, includinginorganic and organic compounds, regardless of the differences in theirstructure, and denotes the phenomenon whereby the initial phase of thematerials in the group mentioned above separates into two phasesmutually different in composition by the effect of thermal processessuitable for the respective conditions. With regard to the forms of suchphase separation, there are two form, one being a binodal decomposition,in which the decomposition is accomplished through a process which canbe regarded as a thermodynamically balanced process (which, in specificterms, is a process consisting of heating and gradual cooling), and theother being a spinodal decomposition which is attained through athermodynamically imbalanced process (which specifically is a processconsisting of heating and quenching). In addition, there is a microphase separation, which occurs typically in such organic compounds ascopolymers. Moreover, the phase separation described above is aphenomenon clearly distinguishable from the thermodynamic viewpoint fromsuch phenomena as segregation, peritectogenesis and eutectogenesis asknown in the field of metallurgy, and, with reference to the phasediagram, it is a phenomenon which appears typically in such diagrams asthose called miscibility gap or solubility gap, which does not includeany invariant reaction.

The materials which compose the recording film according to the presentinvention are those materials which have properties subject to theoccurrence of a binodal decomposition or a spinodal decomposition bysuch means as light and heat--for example, such inorganic compounds asalloys, oxides, halogenides, and non-stoichiometric compounds, blends ofpolymers, which can be regarded as matters composed of two constituents,such organic compounds commonly called "polymer alloys", and thosematerials which have properties subject to the occurrence of a microphase separation by such means as light and heat--for example, suchrandom copolymers, alternate copolymers, block copolymers, graftcopolymers, stoichiometric high molecular compounds, and so forth.

At this point, a detailed description is made of the "binodaldecomposition" and the "spinodal decomposition" mentioned above, withreference to the accompanying drawings.

First, FIG. 6 presents a graph showing the variation in the differenceof free energy (ΔG) to χ in the homogeneous mixture system and theheterogeneous mixture system of a mixture consisting of twoconstituents, i.e., the constituent A in the ratio of χ molar %! and theconstituent B in the ratio of (1-χ) molar %! in their mixture, asobserved at the temperature T_(c) and T₁.

In this graph, the curve for ΔG-χ at the temperature T_(c) indicatesthat the A-B system will be more stable when it is present as ahomogeneous mixture in the entire region of composition, and the ΔG-χcurve at the temperature T₁ indicates that the system, in terms of thecomposition of a and b, will be more stable when it is present in theform of a heterogeneous mixture composed of a and b.

Moreover, the curve (A) shown in solid line in FIG. 7 indicates thelocus as plotted for the temperature at the point a and the point b onthe curve ΔG-χ described above. On the other hand, the curve (B) shownin broken line indicates the locus as plotted for inflection points cand d on the curve ΔG-χ curve given above and demonstrates that thetemperature-composition region enclosed by the curve (A) given above isthe miscibility region.

Then, the temperature-composition region enclosed by the curve (A) andthe curve (B), which are miscibility gap lines, in FIG. 7 is called thebinodal region, and the phase separation in this region progresses bythe binodal decomposition mechanism. This is tantamount to saying that,within this region, only those fluctuations in composition in excess ofa given limit value, among the fluctuations which occur in compositionin a single phase, will survive in a steady state and that thosesurviving fluctuations work as the nuclei for the phase separation,which progresses through the growth of such nuclei. Then, the differencein composition is distinct in the interfacial region between the twophases from the initial stage of the phase separation and, as shown inthe enlarged approximation of an electronic microscope photograph inFIG. 8, the nuclei which have attained growth are set in a sphericalcrystalline structure (or in an amorphous structure in some cases)different in composition from what is found in the original phase andhave the Rayleigh scattering in them. Accordingly, there arises adifference in the reflection factor between the region where this phaseseparation has taken place and the region where the phase separation hasnot occurred, and it becomes possible to perform the optical recordingthrough utilization of this difference in the reflection factor.

On the other hand, the temperature-composition region enclosed by thecurve (B) in FIG. 7 is called "spinodal region" and, within this region,the phase separation progresses by the spinodal decomposition mechanism.That is to say, the minute fluctuations which occur initially in thecomposition in a single phase within this region promote the phaseseparation, which progresses with the predominance of diffusion. Then,in the initial period of the phase separation, the difference in thecomposition in the interfacial region of the two phases is continuous,and, as shown in the enlarged approximation of the electronic microscopephotograph presented in FIG. 9, the phase separation structure assumes aform with the two phases in maze pattern with each other, giving rise tothe Rayleigh scattering in the same way as in the case of the binodaldecomposition. Therefore, also in this case, a difference occurs in thereflection factor between the region where the phase separation hastaken place and the region where it has not occurred, and it isconsequently possible to perform the optical recording process throughutilization of this difference in the reflection factor.

At this juncture, it is noted that the spinodal decomposition does notaccompany any nucleus formation, as compared with the binodaldecomposition, and consequently requires proportionately less energy forthe decomposition, so that the phase separation progresses at a fasterspeed than in the case of the binodal decomposition.

The present invention makes effective use of this property of thespinodal decomposition, and thus the recording process which utilizesthe spinodal decomposition, therefore, offers the advantage that theprocess is capable of performing the recording operation at a speedfaster than the process which uses the phase separation attending thebinodal decomposition.

Furthermore, it is possible to cause the occurrence of the spinodaldecomposition in the region which has already been processed for itsphase separation by the binodal decomposition mechanism, and,conversely, it is possible to cause the occurrence of the binodaldecomposition in the region where the phase separation has already beenelicited by the spinodal decomposition. In specific terms, it ispossible to cause the shift of the region processed by either of theseprocesses to the state of phase separation attained in the other processby restoring the recording film which is in either one of the states tothe state of a single phase by heating it to a temperature higher thanthe miscibility gap line and thereafter causing a binodal decompositionin this recording film by giving a gradual cooling treatment to the filmor causing a spinodal decomposition in the film by giving a quenchingtreatment to it. Then, since there emerges a difference in thereflection factor between the region where the binodal decomposition hasoccurred and that where the spinodal decomposition has taken place, itis possible also to perform optical recording by utilizing thisdifference in the reflection factor, namely, setting the state of phaseseparation in one region in correspondence to the recording state andthe state of phase separation in the other region in correspondence tothe erasing state.

Moreover, in this recording process which utilizes the spinodaldecomposition and the binodal decomposition, it is possible to give thequenching treatment and the gradual cooling treatment to the recordingfilm by switching the output of the irradiating beam. Therefore, thisprocess offers the advantage that the information can be rewritten byone beam by applying a single recording and erasing beam which can thusbe selectively switched over for a change of its output.

Furthermore, in addition to the above-mentioned recording process whichmakes use of the phase separation between the spinodal decomposition andthe binodal decomposition, it is possible to perform the rewriting ofinformation by one beam, for example, also in the process which utilizesthe difference in the optical properties between the amorphous phase ofthe recording material and the phase separation attending the binodaldecomposition in the film. That is to say, it is possible to cause ashift of one state of phase to the other by causing a phase separationattending the binodal decomposition by giving a gradual coolingtreatment to the recording film, or by changing it into its amorphousphase by giving it a quenching treatment, after once restoring therecording film, which is in either one of the states, to its singlephase state by heating it to a temperature higher than its miscibilitygap line. Consequently, it becomes possible to rewrite the informationby one beam, for example, by setting the amorphous phase incorrespondence to the recording state and setting the other state ofphase separation in correspondence to the erasing state.

Furthermore, in case the phase separation is in the course of itsprogress by the binodal decomposition accompanying the nucleus growth,it sometimes happens that the spinodal decomposition progresses inparallel within this nucleus. In this case, a maze pattern structure isobserved within the nucleus, in comparison with the case in which thebinodal decomposition occurs independently, and the reflection factor inthis region where this phase separation has occurred is different fromthat found in the case where the binodal decomposition occurs alone.

Therefore, it is possible also to record tertiary value signals by usingthe differences in the reflection factor among the region where thephase separation has not occurred, the region where the binodaldecomposition and the spinodal decomposition have occurred, and theregion where only the binodal decomposition has occurred.

Next, the miscibility gap mentioned above appears in the solid phaseregion (for example, refer to the phase diagrams or the like given inFIG. 10 through FIG. 14) in some cases and appears in the liquid phaseregion (for example, refer to the phase diagrams or the like given inFIG. 15 through FIG. 17) in other cases in a mixed body composed of twoconstituents as expressed by the constituent A and the constituent B. Incase either one of these recording materials is applied, it is necessaryto set the condition for the irradiation of a laser beam or the like forthe performance of recording at a temperature higher than itsmiscibility gap line.

Here, in case of the application of a recording material for which themiscibility gap appears in the liquid phase region, the recording filmundergoes dissolution by the irradiation of a laser beam set at theprescribed temperature, and the mixture of the two constituents in therecording film is thereby mixed into a state of a single phase, and therecording film is thereafter cooled to shift again to a new state and toattain a phase separation. Thus, this process offers the advantage thatit is capable of rewriting the information by one beam as mentionedabove through adjustment of this cooling speed.

Moreover, according to the present invention, a process which makesdexterous use of the recording material in which this miscibility gapline appears in the liquid phase region and is characterized by itsperformance of the rewriting of information with one beam by irradiatinga single beam for recording and erasing with its output changedselectively.

On the other hand, in case a recording material in which the miscibilitygap mentioned above appears in the solid phase region, the recordingfilm remains in the state of its solid phase even under the temperaturecondition that the temperature in the irradiating conditions of a laserbeam or the like is set at a level higher than the miscibility gap line,and consequently the diffusing speed is so low that the recording filmwill not necessarily form any completely uniform phase, in which case itis not possible to apply the process of rewriting the information withone beam as described above. Therefore, in case any material in whichthe miscibility gap appears in the solid phase region is applied, itwill be made possible to apply the information rewriting process withone beam if the irradiating condition for the laser beam or the like isset at a temperature above the liquid phase region, which is stillhigher than the solid phase region mentioned above. However, in case theinformation rewriting process with one beam is not employed, it is ofcourse feasible to set the irradiating condition for the laser or thelike mentioned above at a temperature within the solid phase region.

Moreover, the materials which cause the binodal decomposition or thespinodal decomposition as described above are alloys and mixturescontaining two or more oxides or halogenides out of the oxides andhalogenides of the individual elements selected out of the followinggroups of elements:

IA group (Li, Na, K, Rb, Cs, Fr)

IIA group (Be, Mg, Ca, Sr, Ba, Ra)

IIIA group (Sc, Y)

IVA group (Ti, Zr, Hf)

VA group (V, Nb, Ta)

VIA group (Cr, Mo, W)

VIIA group (Mn, Tc, Re)

VIIIA group (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt)

IB group (Cu, Ag, Au)

IIB group (Zn, Cd, Hg)

IIIB group (B, Al, Ga, In, Tl)

IVB group (Si, Ge, Sn, Pb)

VB group (As, Sb, Bi)

VIB group (Se, Te, Po)

Lanthanoids

(Ce, Pr, Nd, Pm, Sm, bu, Gd, Tb, Dy, Ho, Br, Yb)

Actinoids

(Ac, Th, Pa)

To name specific materials, the following alloys which have beenascertained to cause the binodal decomposition from the binodal curve(A) in the phase diagrams given in FIG. 10 through FIG. 12 and thefollowing alloys which have been ascertained to cause the spinodaldecomposition from the spinodal curve (B) in the phase diagram given inFIG. 13 can be listed as such materials:

Mixtures of PbTe--GeTe (FIG. 10)

Mixtures of Au--Pt (FIG. 11)

Mixtures of Au--Ni (FIG. 12)

Mixtures of PbS--PbTe (FIG. 13) and

Mixtures of GeSe₂ --GeSe

(For example, Ge₄₁.25 Se₅₈.75)

Mixtures of As--Ge--Te

(For example, As₄ Ge₁₅ Te₈)

Also, the following materials, which are oxide-oxide mixtures that havebeen ascertained to cause the binodal decomposition or the spinodaldecomposition in light of the literature cited in the brackets:

Mixtures of Li₂ O--SiO₂

(Y. Moriya, D. H. Warrington, and R. W. Douglas, Phys. Chem. Glasses,8,19, (1967))

Mixtures of Na₂ O--SiO₂

(Y. Moriya, D. H. Warrington, and R. W. Douglas, Phys. Chem. Glasses,8,19, (1967))

Mixtures of BaO--SiO₂

(T. P. Seward, D. R. Uhlmaznn, and D. Turnbull, Phys. Chem. Glasses,51,278 (1967))

Mixtures of Al₂ O₃ --SiO₂

(J. F. Macdowell and G. H. Beal, J. Am. Ceram. Soc., 52,17 (1969))

Mixtures of B₂ O₃ --SiO₂

(R. J. Charles and F. G. Wagstagg, J. Am. Ceram. Soc., 51,16 (1968))

Mixtures of Li₂ O--B₂ O₃

(R. R. Shaw and D. R. Uhlmann, J. Am. Ceram. Soc., 51,377 (1968))

Mixtures of Na₂ O--B₂ O₃

(R. R. Shaw and D. R. Uhlmann, J. Am. Ceram. Soc., 51,377 (1968))

Mixtures of K₂ O--B₂ O₃

(R. R. Shaw and D. R. Uhlmann, J. Am. Ceram. Soc., 51,377 (1968))

Mixtures of Rb₂ O--B₂ O₃

(R. R. Shaw and D. R. Uhlmann, J. Am. Ceram. Soc., 51,377 (1968))

Mixtures of Cs₂ O--B₂ O₃

(R. R. Shaw and D. R. Uhlmann, J. Am. Ceram. Soc., 51,377 (1968))

Mixtures of PbO--B₂ O₃

(J. H. Simons, J. Am. Ceram. Soc., 56,286 (1973))

Also, the following materials which are mixtures of oxide-oxide andascertained to cause the phase separation from the miscibility gap line(A) in the phase diagrams given in FIG. 14 through FIG. 30 can be listedas such materials:

Mixtures of ZrO₂ --ThO₂ (FIG. 14)

Mixtures of CaO--SiO₂ (FIG. 15)

Mixtures of B₂ O₃ --PbO (FIG. 16)

Mixtures of B₂ O₃ --V₂ O₃ (FIG. 17)

Mixtures of SnO₂ --TiO₂ (FIG. 18)

Mixtures of NiO--CoO (FIG. 19)

Mixtures of Al₂ O₃ --Cr₂ O₃ (FIG. 20)

Mixtures of SiO₂ --Al₂ O₃ (FIG. 21)

Mixtures of ZnWO₄ --MnWO₄ (FIG. 22)

Mixtures of CaWO₄ --NaSm(WO₄)₂ (FIG. 23)

Mixtures of CaWO₄ --Sm₂ (WO₄)₃ (FIG. 24)

Mixtures of MnMoO₄ --ZnMoO₄ (FIG. 25)

Mixtures of Fe₂ TiO₄ --Fe₃ O₄ (FIG. 26)

Mixtures of Ca₃ Cr₂ Si₃ O₁₂ --Ca₃ Fe₂ Si₃ O₁₂ (FIG. 27)

Mixtures of 65MgSiO₃ /35FeSiO₃ --CaSiO₃ (FIG. 28)

Mixtures of LiAl₅ O₈ --LiFe₅ O₈ (FIG. 29)

Mixtures of NaAlSi₃ O₈ --KAlSi₃ O₈ (FIG. 30)

In addition to these group of materials, the following mixture is to belisted:

Mixtures of Na₂ O--B₂ O₃ --SiO₂

In addition, the following materials containing halogenide-halogenidemixtures which have been ascertained to cause the phase separation fromthe miscibility gap line (A) given in the phase diagrams presented inFIG. 31 through FIG. 45 can be listed as such materials:

Mixtures of LiCl--NaCl (FIG. 31)

Mixtures of KCl--NaCl (FIG. 32)

Mixtures of CsCl--TlCl (FIG. 33)

Mixtures of CaCl₂ --MnCl₃ (FIG. 34)

Mixtures of CaCl₂ --SrCl₂ (FIG. 35)

Mixtures of LiBr--AgBr (FIG. 36)

Mixtures of AgBr--NaBr (FIG. 37)

Mixtures of KBr--NaBr (FIG. 38)

Mixtures of TlBr--CsBr (FIG. 39)

Mixtures of KI--NaI (FIG. 40)

Mixtures of NaI--CaI₂ (FIG. 41)

Mixtures of (GaI₂)₂ --NaGaI₄ (FIG. 42)

Mixtures of (GaI₂)₂ --KGaI₄ (FIG. 43)

Mixtures of (GaI₂)₂ --RbGaI₄ (FIG. 44)

Mixtures of GaAlI₄ --Ga₂ I₄ (FIG. 45)

Also, as materials causing the binodal decomposition or the spinodaldecomposition mentioned above, it is possible to list thenon-stoichiometric compounds of oxides, halogenides, and so forth.

Here, the term "non-stoichiometric compounds" means those compoundswhich are composed of the element M and the element X and yet have theircomposition deviating from the standard ratios, and, in the case ofthose non-stoichiometric compounds in which the element M and theelement X are compounded in the ratio of (m-δ) versus n (wherein, m andn express positive integral numbers while δ expresses a number whichsatisfies the relation, 0<δ<1), δ represents th extent of the deviationfrom the standard ratios of composition and is accordingly called the"non-stoichiometric ratios". Such a deviation from the standard ratiosof composition occurs in consequence of a lattice defect present ineither the element M or the element X. In case the lattice defect is inthe form of a void lattice, for example, in the element, attractionworks between void lattices, and this is one factor accountable for thefact that such a non-stoichiometric compound assumes propertiesdifferent from those of the regular stoichiometric compound.

Then, in such a non-stoichiometric compound, the element M and theelement X, which constitute the compound, can be regarded as forming amixture consisting of the two constituents, and such compounds cause thebinodal decomposition or the spinodal decomposition in the same way asthe recording materials mentioned above. That is to say, suchnon-stoichiometric compounds cause the occurrence of the binodaldecomposition or the spinodal decomposition by the effect of a change intemperature and undergo their phase separation between the phase withmore void lattice points and the phase with less of such lattice points(that is to say, between two phases with differences in theirnon-stoichiometric ratios).

To form such non-stoichiometric compounds, it is possible to apply anycompound formed of at least one of the metal elements as selected out ofthe following list:

Beryllium (Be), Boron (B), Magnesium (Mg), Aluminium (Al), Silicon (Si),Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Manganese(Mn), Iron (Fe), Cobalt (Co), Nickel (Ni), Copper (Cu), Zinc (Zn),Gallium (Ga), Germanium (Ge), Arsenic (As), Selenium (Se), Rubidium(Rb), Yttrium (Y), Zirconium (Zr), Niobium (Nb), Molybdenum (Mo),Technetium (Tc), Ruthenium (Ru), Rhodium (Rh), Palladium (Pd), Silver(Ag), Cadmium (Cd), Indium (In), Tin (Sn), Antimony (Sb), Tellurium(Te), Hafnium (Hf), Tantalum (Ta), Tungsten (W), Rhenium (Re), Osmium(Os), Iridium (Ir), Platinum (Pt), Gold (Au), Thallium (Tl), Lead (Pb),Bismuth (Bi), Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Promethium(Pm), Samarium (Sm), Europium (Eu), Gadolinium (Gd), Terbium (Tb),Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium(Yb), Lutetium (Lu), and Uranium (U)

and at least one element selected out of the following: Oxygen (O),Sulfur (S), Nitrogen (N), Hydrogen (H), Iodine (I), Bromine (Br), andChlorine (Cl).

Moreover, such inorganic materials which show a monotonous curve with aconvex upward contour in relation to temperature as observed in thephase diagram usually have the miscibility gap mentioned above and canbe applied as recording material for the present invention.

Then, as specific examples of the non-stoichiometric compounds andinorganic materials mentioned above, it is possible to list suchrecording material groups as the following material groups which havebeen ascertained to cause the phase separation in light of themiscibility gap line (A) in the phase diagrams presented in FIG. 46through FIG. 48:

CeO_(h) group (FIG. 46)

Mixtures of Bi--Bi₂ O₃ (FIG. 47)

Mixtures of CaCO₃ --MnCO₃ (FIG. 48)

Moreover, as organic materials applicable as the recording materialsmentioned above, there are polymer blends called "polymer alloys", whichcause the occurrence of the binodal decomposition or the spinodaldecomposition, and random copolymers, alternate copolymers, blockcopolymers, graft copolymers, and stoichiometric high molecularcompounds, which cause a micro phase separation.

The following is a description of a case in which an inorganic recordingmaterial is applied. The inorganic material mentioned above which causesthe binodal decomposition or the spinodal decomposition is coated in theform of a film on the substrate and this film is conditioned to assume asingle crystalline state or amorphous state, and this conditionedrecording film is then irradiated with a beam of light or heat toachieve a phase separation thereof, and, with a change made in thereflection factor in this region, information is written to the film, sothat the film is available for use as an optical recording medium foruse exclusively for recording and reproduction, or, with a beam of lightor heat being irradiated on the region where the phase separation isthus achieved, the irradiated region is caused to undergo dissolution,and, by restoring this dissolved region to its initial state, the filmis available for use as an optical recording medium for use inrecording, reproduction, and erasure.

Moreover, in case an inorganic recording material which has amiscibility gap appearing in its liquid phase region is applied, or incase an inorganic recording material which has a miscibility gapappearing in its solid phase region is used and yet the irradiatingcondition of the laser beam or the like is set at a temperature abovethe level of its liquid phase region, it is possible to apply theinformation rewriting system with one beam as described above.

On the other hand, in the case in which an organic recording material isapplied, which is described below, the organic material which causes thebinodal decomposition or the spinodal decomposition or a micro phaseseparation is coated in the form of a film on the substrate andconditioned to the state of a single phase, and, with a beam of light orheat irradiated on the recording film as so conditioned, the film iscaused to have selective phase separation, and, with information writtento the film through utilization of the changes in the reflection factorin this irradiated region, the recorded film thus processed is offeredfor use as an optical recording medium exclusively in recording andreproduction, or, with the beam of light or heat or the like beingirradiated on this region where the phase separation has thus beenproduced, the irradiated region of the film is caused to undergo itsdissolution, thereby being restored to its initial state, and the filmso prepared is offered for use as an optical recording medium forrecording, reproduction, and erasure.

At this juncture, the materials for the substrate which is used for theformation of the recording film mentioned above are glass and suchlight-transmissive resin materials as acrylic resin, polycarbonate, andepoxy resin for the type of process in which a beam of light isirradiated from the substrate side. On the other hand, such metalmaterials as aluminium can be used in the type of process in which abeam of light is irradiated from the side opposite to the substrate.Moreover, in case resin material is used for the substrate, it isfeasible to set up a heat interfering layer composed, for example, ofSiO₂, ZrO₃, and ZnS between the substrate and the recording film inorder to thereby prevent the thermal damages of the substrate. If a heatinterfering layer made of SiO₃ or the like and having heat radiatingeffect is installed in a position adjacent to the recording film, it ispossible to give high temperature heating and quenching treatments tothe recording film and consequently it is made possible to apply thepresent invention which utilizes the phase separation attending thespinodal decomposition as the means of recording the information.

Furthermore, a protective film layer composed of the material formingthe above-mentioned heat interfering layer or any such materials asresin hardened by the ultraviolet rays, acrylic resin, polycarbonate,and epoxy resin may be coated over the recording film for the purpose ofprotecting its surface. In addition, a highly refractive layer made ofZnS or the like may be formed on the surface of the recording film forthe purpose of increasing the quantity of light to be reflected from therecording film mentioned above.

Next, with regard to the means of coating on the substrate the recordingfilm composed of inorganic material having such properties as cause thebinodal decomposition or the spinodal decomposition, it is possible toapply such processes as the thermal vaporization process, the ionplating process, the reactive sputtering process, the chemical vaporphase deposition process (CVD), the ion-aided deposition process (IAD),and the molecular beam epitaxial process (MBE). On the other hand, withregard to the means of coating an the substrate the recording filmcomposed of organic material having such properties as cause theoccurrence of the binodal decomposition, the spinodal decomposition, orthe micro phase separation, it is feasible to form the film by havingthe copolymers or the like perform their polymerizing reaction directlyon the substrate or to dissolve such copolymers into their secondarycompound and to coat the compound on the substrate by some appropriatemeans.

In this regard, the technical means of accomplishing this is applied tothe recording, reproducing, and erasing type of the recording film sinceit is capable of rewriting the recorded information. Yet, in view of thefavorable stability in the maintenance of the recorded information, themeans according to the present invention can, of course, be applied alsoto the recording and reproducing type of the recording film, asdescribed above.

According to the present invention, the recording film is caused toundergo the phase separation by such means as light and heat, so thatthe optical properties in the processed region are changed. Therefore,the recording film is not susceptible to changes in the recording filmwith the passage of time, and it is consequently capable of maintainingthe state of its phase separation over a long period of time.

Further, according to the present invention, the recording film isformed of such recording material as has a miscibility gap lineappearing in its liquid phase region as observed in the phase diagramand the recording film also performs the rewriting of information with asingle recording-erasing beam with selectively changeable output, whichis irradiated on the surface of the above-mentioned recording film, sothat the present invention attains simplification in the rewritingoperation.

Furthermore, according to the present invention, a heat interfering filmhas a heat radiating effect and is positioned in the region adjacent tothe recording film and causes the recording film to have its phaseseparation attending the spinodal decomposition by the high temperatureheating and quenching treatments applied to the recording film.Therefore, the present invention achieves a reduction of the timerequired for the phase separation.

The present invention has the advantage of the maintenance of the stateof phase separation in the recording films of the present invention overa long period of time as discussed below. Specifically, if the region ofthe recording film where the phase separation has occurred is to resumeits original state, it is necessary for the considerably large number ofatoms to attain their diffusion over a considerable distance. However,for the recording film which is in the state of its solid phase at leastunder the room temperature, the speed of diffusion of the atoms of whichthis recording film is composed is extremely low and their diffusiondoes not occur in their groups. It is primarily conceivable that thesefactors are accountable for the point that the recording film mentionedabove is less susceptible to change over time.

Also, in light of the fact that secular changes occur in the phasechange type recording material by the effect of minute fluctuations inthe arrangement among the adjacent atoms in it, it is possible to inferthat the recording film according to the present invention is not liableto changes over the passage of time.

Referring to the drawings, preferred embodiments of the presentinvention will now be described with reference to the accompanyingdrawings.

FIRST EXAMPLE

Now, the optical recording medium used in this first example ofpreferred embodiments has its principal parts constructed, as shown inFIG. 1, with a heat-resistant plastic (polycarbonate) substrate (1) witha thickness of 1.2 mm and a diameter of 51/4 inches (ISO standard), aheat interfering layer (2) made of SiO₂ in the thickness of 1000 Å andcoated on the surface of the substrate (1), and a recording film (3)made of a mixture of LiO₂ and SiO₂ formed on the surface of this heatinterfering layer (2).

In this regard, the recording film (3) is coated on the heat interferinglayer (2) on the substrate (1) by depositing a mixture of (LiO₂)₂₅ and(SiO₂)₇₅ thereon by applying the sputtering process using two targetsLiO₂ and SiO₂ and by conditioning the formed film to the crystallinestate in a single phase.

Then, the optical recording medium is rotated at 1,800 rpm, and, whilethe medium is kept in this state, a laser beam with an output of 10 mWand a frequency of 3.7 MHz is irradiated onto the recording region ofthe recording film (3), and, with the temperature in the irradiatedregion of the recording film (3) being set at the temperature for themiscibility region as shown in the phase diagram given in FIG. 2, thebinodal decomposition is caused to occur in the partial region of therecording film, so that the film undergoes its selective phaseseparation in the region, and information is written to the region bythe effect of the changes in the reflection factor in the region.

For reproduction, the optical recording medium mentioned above isrotated at 1,800 rpm, and, in this state, a laser beam with the outputof 1 mW is irradiated onto the recording film (3), and the reflectedbeam thereof is read by the light receiving element, and thereproduction of the information is thereby performed. The C/N ratio ofthe reproduced signal was 50 dB.

Moreover, this optical recording medium has been applied as a recordingmedium for its use exclusively in recording and reproduction.

SECOND EXAMPLE

The optical recording process as described in this example of preferredembodiments is approximately the same as in the optical recordingprocess shown in the first example of the preferred embodiments, exceptthat this process uses an optical recording medium which is providedadditionally with a layer (4) with a high index of refraction, beingmade of ZnS, a material with a high index of refraction, over therecording film (3) mentioned above.

Therefore, this example not only has the same advantages as those of thefirst example of preferred embodiments, but also offer the additionaladvantage that it achieves an improvement on the C/N ratio of thereproduced signals to 53 dB (whereas the C/N ratio is 50 dB in the firstexample) because it can secure an increased quantity of light from therecording film (3) owing to the effect of the layer (4) with a highindex of refraction mentioned above.

THIRD EXAMPLES

The optical recording process described in this example of preferredembodiments is approximately the same as the process described in thefirst example, except that the recording film (3) of the opticalrecording medium (Refer to FIG. 4) used in this process is composed ofTeO_(x), which is a non-stoichiometric compound, and that this recordingfilm (3) is formed directly on the substrate (1).

Here, the recording film (3) mentioned above is prepared by coatingTeO_(x) on the substrate (1) by the RF ion plating process using a Tetarget in the state in the atmosphere of oxygen gas and by conditioningthe film to assume a crystalline state in a single phase.

In this regard, the mark x as used in TeO_(x) given above has the value,x=1.75.

Moreover, the conditions for setting the RF ion plating process are asfollows:

    ______________________________________    Target vaporizing process:                       Resistance heating                       Electron beam vaporization    Atmosphere:    Ar pressure        1 × 10.sup.-2 to 1 Pa    O.sub.2 pressure   1 × 10.sup.-2 to 1 Pa    RF power:          100 to 1,000 KW    Rate:              0.5 to 10A/sec.    ______________________________________

Moreover, for the operation for writing information to the opticalrecording medium mentioned above, the optical recording medium isrotated at 1,800 rpm, and, in this state, a laser beam with an output of6 mW at the frequency of 3.7 MHz is irradiated onto the recording regionof the recording film (3), and, after the recording film (3) in theirradiated region is once dissolved, it is cooled down to cause thebinodal decomposition, so that the processed region of the film has aselective phase separation, and the writing of information to therecording medium is thus performed.

On the other hand, this process performs the reproduction of therecorded information by rotating the above-mentioned optical recordingmedium at 1,800 rpm and irradiating, while the medium is kept in thisstate, a laser beam with an output of 1 mw onto the recording film (3)of the medium and reading the reflected light of the beam by means ofthe light receiving element. The C/N ratio of the reproduced signal is55 dB.

The fact that the recording film (3) formed of TeO_(x) has the phaseseparation occurring in it has been ascertained on the basis of theobservation that the structure in the irradiated region as viewed in aTEM photograph (a photograph taken under a transmissive type electronicmicroscope) exhibits a structure peculiar to the binodal decomposition.

As a result, the optical recording process as described in this exampleof preferred embodiments has an excellent advantage in stability for themaintenance of the recorded information, and, above all, it attains aC/N ratio in the reproduced signals at the level of 55 dB, as mentionedabove. Thus, the process in this example has proved to be superior tothe process described in the second example of preferred embodiments(The process in the second example recorded a C/N ratio at 53 dB).

Moreover, this optical recording medium is applied exclusively forrecording and reproduction.

FOURTH EXAMPLE

The optical recording process described in this example of preferredembodiments is almost the same as the recording process described in thethird example of preferred embodiments, except for the point that thisprocess is provided with a heat interfering layer (2) made of SiO₂ onits substrate, as shown in FIG. 5, and that it uses an optical recordingmedium with a recording film (3) made of TeO_(x) coated on the surfaceof this heat interfering layer (2). Thus, the optical recording mediumof which the recording film (3) mentioned above is conditioned to assumea crystalline state in a single phase is rotated at 1,800 rpm, and,while the recording film is kept in this state, a laser beam with anoutput of 10 mW and a frequency of 3.7 MHz is irradiated onto therecording region of the recording film (3), so that the recording film(3) in the irradiated region is once dissolved and thereafter cooled tocause a selective phase separation therein, and information is thuswritten to the recording film.

This optical recording medium is applied exclusively in recording andreproduction in the same way as in the third example of preferredembodiments.

In this example, the output from the beam in the writing process is ashigh as 10 mW for the operation in which information is written by theirradiation of the laser beam onto the surface of the recording film (3)of the optical recording medium mentioned above, and, unlike the opticalrecording medium described in the third example, the medium in thisexample is provided with a heat interfering layer (2). By the heatradiating effect of this heat interfering layer (2), the temperature inthe recording film in the irradiated region is cooled more sharply thanin the case of the third example of preferred embodiments. Consequently,rather than the binodal decomposition, the spinodal decomposition occursin the irradiated region of the recording film in this example.

Therefore, in contrast with the optical recording process in the thirdexample, which is performed through utilization of the feature that thereflection factor in the region where the binodal decomposition hasoccurred becomes lower than in the other region, the optical recordingprocess in this example is performed through utilization of the featurethat the reflection factor in the region where the spinodaldecomposition has occurred will be higher than in the other region.

The optical recording process described in this example of preferredembodiments also offers the advantage that it has excellent stabilityfor the maintenance of recorded information as is the case with theprocesses in the other examples, and, in addition, this process hasrecorded 50 dB in the C/N ratio of the reproduced signal, thus marking avalue higher than that achieved in the existing process.

Furthermore, the optical recording process described in this exampleperforms the recording of information through utilization of the phaseseparation attending the spinodal decomposition and consequently offersthe additional advantage that it can operate at a higher writing speedthan in the process described in the third example.

FIFTH EXAMPLE

The optical recording process described in this example is almost thesame as the process in the fourth example, except that this processapplies the optical recording medium described in the fourth example andthat this process performs the rewriting of information with one beamthrough its utilization of the phase separation between the spinodaldecomposition and the binodal decomposition in the recording film (3).In this case, the phase separation attending the spinodal decompositionis set in correspondence with the recording state while the phaseseparation attending the binodal decomposition is set in correspondencewith the erasing state. That is to say, the optical recording medium inwhich the recording film (3) is conditioned to assume a crystallinestate in a single phase is rotated at 1,800 rpm, and, while the mediumis held in this state, a laser beam with an output of 8 mw and afrequency of 3.7 MHz is irradiated uniformly over the surface of therecording film (3) mentioned above and the recording film (3) is therebydissolved once. Then, the recording film (3) is gradually cooled, bywhich a phase separation attending the binodal decomposition is eliciteduniformly in the recording film (3), and its initialization is therebyeffected.

Next, with the initialized optical recording medium being rotated at1,800 rpm, and, while the medium is kept in this state, a laser beam anthe output of 10 mW and a frequency of 3.7 MHz is irradiated onto therecording region on the recording film (3) mentioned above, and therecording film (3) in the irradiated region is thereby dissolved onceand thereafter cooled sharply, by which the said recording film iscaused to have a phase separation attending the spinodal decomposition,and the writing of information is performed in this state of the film.

For reproduction, the optical recording medium to which information hasbeen thus written is rotated at 1,800 rpm, and, while the said medium iskept in this state, a laser beam with an output of 1 mW is irradiatedonto the recording film (3) of the medium and also the reflected beam isread by the light receiving element, the reproduction of the recordedsignal being thereby performed. Moreover, the C/N ratio of thereproduced signal is almost the same as that recorded in the fourthexample of preferred embodiments.

Moreover, for the rewriting of the information written to the opticalrecording medium mentioned above, this optical recording medium isrotated at 1,800 rpm, and, while the medium is kept in this state, asingle recording-erasing laser beam (with an output of 10 mW forrecording, an output of 8 mW for erasing, and a frequency of 3.7 MHz)which can be selectively switched for different output levels isirradiated onto the said recording film, by which the rewriting of therecorded information is performed.

The optical recording process described in this example of preferredembodiments also has excellent stability for the maintenance of therecorded signal in the same way as in the processes in the otherexamples of preferred embodiments, and this process exhibits a high C/Nratio of the reproduced signal as compared with the value attained bythe existing process.

Furthermore, the optical recording process described in this example ofpreferred embodiments performs the writing and rewriting of informationby one beam using the phase separation between the spinodaldecomposition and the binodal decomposition, and this process thereforeoffers the advantage that it is capable of rewriting the recordedinformation and that it can perform this with simpler operation ascompared with the case of the processes described in the other examples.

SIXTH EXAMPLE

The optical recording process described in this example of preferredembodiments is almost the same as the process in the first example ofpreferred embodiments, except that the recording film for the opticalrecording medium used in this process is composed of tri-block copolymercoated directly on the substrate and causes the occurrence of the microphase separation.

Here, the recording film mentioned above is formed directly into a filmby the living copolymerizing process of a tri-block copolymer in thestructure, (polystyrene)--(polyisoprene)--(polystyrene), and isconditioned to be in the single phase state. Here, instead of thisfilm-forming process, it is also feasible to form a recording film setin the state of a single phase by once dissolving the tri-blockcopolymer mentioned above into such a solvent as alcohol and applyingthe solution by spin coating to the surface of the substrate andthereafter forming a recording film set in the state of a single phaseby evaporating the above-mentioned solvent, such as alcohol.

Then, the operation for the writing of information to the opticalrecording medium mentioned above is performed by rotating the opticalrecording medium at 1,800 rpm and, while keeping the medium in thisstate, irradiating the recording region of the recording film with alaser beam with an output of 7 mW and a frequency of 3.7 MHz, and oncedissolving the recording film in the irradiated region and thereaftercooling the film, thereby selectively causing a micro phase separationto occur in the film.

The reproduction of the recorded information is performed by rotatingthe optical recording medium mentioned above at 1,800 rpm andirradiating a laser beam with an output of 0.8 mW to the recording film(3) of the recording medium, while the recording medium is kept in thisstate, and causing the light receiving element to read the reflectedlight of this beam.

This optical recording medium has been applied as a recording mediumexclusively in the recording and reproduction of information.

This optical recording process described in this example of preferredembodiments also has the advantage that it is excellent in the stabilityfor the maintenance of the recorded information, and this process hasalso proved to produce a favorable C/N ratio of the reproduced signal.

SEVENTH EXAMPLES

The optical recording process described in this example is almost thesame as the process described in the fifth example, except that theoptical recording medium used in this process is composed of a blend ofthe following polymers which are placed to form a coat of film on thesubstrate and cause the spinodal decomposition and the binodaldecomposition, depending on the cooling condition applied to them. Inthis case, moreover, the phase separation attending the binodaldecomposition is set in correspondence with the recording state whilethe phase separation attending the spinodal decomposition is set incorrespondence with the erasing state.

At this juncture, the recording film mentioned above has been formedinto a film by coating the polymer blend of(polystyrene)--(polyisoprene) dissolved in acetone on the substrate andconditioning the film to assume the state of a single phase.

The recording film (3) as adjusted to the state of a single phase isrotated at 1,800 rpm, and a laser beam with an output of 8 mW and afrequency of 3.7 MHz is irradiated uniformly over the surface of therecording film (3) mentioned above, the recording film being therebyonce dissolved, and thereafter the film is quenched and thereby causedto undergo a uniform phase separation attending the spinodaldecomposition, and the initialization of the recording film (3) is thuseffected.

Next, the initialized optical recording medium is rotated at 1,800 rpm,and, while the medium is kept in this state, a laser beam with an outputof 6 mW and a frequency of 3.7 MHz is irradiated onto the recordingregion of the recording film (3) mentioned above, thereby oncedissolving the recording film (3) in the irradiated region. Thereafter,the region is gradually cooled, which causes a phase separationattending the binodal decomposition, and the writing of information isthus performed.

For reproduction, the optical recording medium containing theinformation written to it is rotated at 1,800 rpm, and, with the mediumkept in this state, a laser beam with an output of 0.8 mW is irradiatedon the recording film (3) of the medium and the reflected beam is readwith the light receiving element, and the reproduction of the recordedinformation is thus performed.

In case the information written to the optical recording mediummentioned above is to be rewritten, the optical recording medium isrotated at 1,800 rpm, and, while this recording medium is kept in thisstate, the rewriting of the recorded information is performed byirradiating a single erasing beam (with an output of 6 mW for recording,an output of 8 mW for erasing, and a frequency of 3.7 MHz), which can beswitched selectively for generating variable output, onto the recordingfilm of the recording medium.

This optical recording process described in this example of preferredembodiments also has the advantage that it has excellent stability forthe maintenance of the recorded information, in the same way as in thecase of the other examples of preferred embodiments, and this processalso attains a high C/N ratio of the reproduced signal in comparisonwith the value recorded by the existing process.

Furthermore, the optical recording process described in this example ofpreferred embodiments performs the writing and rewriting of informationthrough utilization of the phase separation between the spinodaldecomposition and the binodal decomposition in the same manner as in thefifth example of preferred embodiments, and this process, therefore,offers the advantage that it is capable of performing the rewriting ofthe information and also offers simplicity and convenience in itsoperation, as compared with the processes described in the otherexamples of preferred embodiments.

According to the present invention, the recording film undergoes itsselective phase separation by applying such means as light and heat,thereby producing changes in the optical properties of the processedregion. Therefore, the recording film mentioned above is not susceptibleto the occurrence of changes in its state over the passage of time, sothat it becomes possible to maintain the state of the phase separationover a long period of time and, consequently, the recorded informationfor a long time.

Further, according to the present invention, a recording film ofmaterial having its miscibility gap line appearing in its liquid phaseregion as seen in the phase diagram enables the performance of therewriting of the recorded information with one beam by irradiating asingle record-erasing beam having an output which can be changedselectively. Therefore, this process offers the advantage that therewriting operation is thereby simplified.

Furthermore, the present invention provides a heat interfering layerhaving a heat radiating effect in a position adjacent to the recordingfilm and causes the recording film to undergo its phase separationattending its spinodal decomposition by applying high temperatureheating and quenching treatments to the recording film. Thus, thisprocess achieves a reduction in the duration of time required for thephase separation and can therefore accomplish the advantageous effectthat it improves the rewriting speed.

What is claimed is:
 1. A method for recording information to a recordingmedium comprising:a substrate having a surface; and a recording filmformed on said surface, said recording film having optical propertiesthat change in response to the application of a light beam or heat to aportion of said recording film and subsequent cooling of said recordingfilm, wherein said recording film comprises an inorganic mixture,wherein said inorganic mixture is a mixture selected from the groupconsisting of Au--Pt, Au--Ni, PbS--PbTe, and GeSe₂ --GeSe; said methodcomprising the steps of:applying at least one of a light beam and heatonto said recording film; and cooling said recording film to cause aselective phase separation in a portion of said recording film to whichat least one of said light beam and said heat is applied; wherein saidselective phase separation is caused by a binodal and/or spinodaldecomposition; wherein said binodal decomposition results from theapplication of said light beam or said heat and subsequent gradualcooling; and wherein said spinodal decomposition results from theapplication of said light beam or said heat and subsequent quenchingtreatment.
 2. A method for recording information to a recording mediumas claimed in claim 1, wherein a temperature of said heating higher thana temperature of a miscibility gap line observed in a phase diagram isapplied to said recording film.
 3. The method for recording informationin a recording medium as claimed in claim 1, wherein said recording filmis made of a recording material having miscibility gap line appearing ina solid phase observed in a phase diagram.
 4. The method for recordinginformation in a recording medium as claimed in claim 1, wherein saidrecording film is made of a recording material having a miscibility gapline appearing in a liquid phase observed in a phase diagram.
 5. Themethod for recording information in a recording medium as claimed inclaim 1, wherein said recording film are composed of elements which arecompounded in a ratio of (m-δ) to n in which m and n express positivenumbers while δ expresses a number which satisfies a relation, 0<δ<1. 6.A method for recording information to a recording medium comprising:asubstrate having a surface; and a recording film formed on said surface,said recording film having optical properties that change in response tothe application of a light beam or heat to a portion of said recordingfilm and subsequent cooling of said recording film, wherein saidrecording film comprises an inorganic mixture, wherein said inorganicmixture is a mixture selected from the group consisting of Li₂ O--SiO₂,Na₂ O--SiO₂, BaO--SiO₂, Al₂ O₃ --SiO₂, B₂ O₃ --SiO₂, Li₂ O--B₂ O₃, Na₂O--B₂ O₃, K₂ O--B₂ O₃, Rb₂ O--B₂ O₃, Cs₂ O--B₂ O₃, PbO--B₂ O₃, ZrO₂--ThO₂, CaO--SiO₂, B₂ O₃ --V₂ O₅, SnO₂ --TiO₂ NicO--CoO, Al₂ O₃ --Cr₂O₃, ZnWO₄ --MnWO₄, CaWO₄ --NaSm(WO₄)₂, CaWO₄ --Sm₂ (WO₄)₃, MnMoO₄--ZnMoO₄, Fe₂ TiO₄ --Fe₃ O₄, Ca₃ Cr₂ Si₃ O₁₂ --Ca₃ Fe₂ Si₃ O₁₂, 65MgSiO₃/35FeSiO₃ --CaSiO₃, LiAl₅ O₈ --LiFe₅ O₈, NaAlSi₃ O₈, and Na₂ O--B₂ O₃--SiO₂ ; said method comprising the steps of:applying at least one of alight beam and heat onto said recording film; and cooling said recordingfilm to cause a selective phase separation in a portion of saidrecording film to which at least one of said light beam and said heat isapplied; wherein said selective phase separation is caused by a binodaland/or spinodal decomposition; wherein said binodal decompositionresults from the application of said light beam or said heat andsubsequent gradual cooling; and wherein said spinodal decompositionresults from the application of said light beam or said heat andsubsequent quenching treatment.
 7. A method for recording information toa recording medium as claimed in claim 6, wherein a temperature of saidheating higher than a temperature of a miscibility gap line observed ina phase diagram is applied to said recording film.
 8. The method forrecording an information in a recording medium as claimed in claim 6,wherein said recording film is made of a recording material having amiscibility gap line appearing in a solid phase observed in a phasediagram.
 9. The method for recording information in a recording mediumas claimed in claim 6, wherein said recording film is made of arecording material having a miscibility gap line appearing in a liquidphase observed in a phase diagram.
 10. The method for recordinginformation in a recording medium as claimed in claim 6, wherein saidrecording film are composed of elements which are compounded in a ratioof (m-δ) to n in which m and n express positive numbers while δexpresses a number which satisfies a relation, 0<δ<1.
 11. A method forrecording information to a recording medium comprising:a substratehaving a surface; and a recording film formed on said surface, saidrecording film having optical properties that change in response to theapplication of a light beam or heat to a portion of said recording filmand subsequent cooling of said recording film, wherein said recordingfilm comprises an inorganic mixture, wherein said inorganic mixture is amixture selected from the group consisting of LiCl--NaCl, KCl--NaCl,CsCl--TlCl, CaCl₂ --SrCl₂, LiBr--AgBr, AgBr--NaBr, KBr--NaBr,TlBr--CsBr, KI--NaI, NaI--CaI₂, (GaI₂)₂ --NaGaI₄, (GaI₂)₂ --KGaI₄,(GaI₂)₂ --RbGaI₄, and GaAlI₄ --Ga₂ I₄ ; said method comprising the stepsof:applying at least one of a light beam and heat onto said recordingfilm; and cooling said recording film to cause a selective phaseseparation in a portion of said recording film to which at least one ofsaid light beam and said heat is applied; wherein said selective phaseseparation is caused by a binodal and/or spinodal decomposition; whereinsaid binodal decomposition results from the application of said lightbeam or said heat and subsequent gradual cooling; and wherein saidspinodal decomposition results from the application of said light beamor said heat and subsequent quenching treatment.
 12. A method forrecording information to a recording medium as claimed in claim 11,wherein a temperature of said heating higher than a temperature of amiscibility gap line observed in a phase diagram is applied to saidrecording film.
 13. The method for recording information in a recordingmedium as claimed in claim 11, wherein said recording film is made of arecording material having a miscibility gap line appearing in a solidphase observed in a phase diagram.
 14. The method for recordinginformation in a recording medium as claimed in claim 11, wherein saidrecording film is made of a recording material having a miscibility gapline appearing in a liquid phase observed in a phase diagram.
 15. Themethod for recording information in a recording medium as claimed inclaim 11, wherein said recording film are composed of elements which arecompounded in a ratio of (m-δ) to n in which m and n express positivenumbers while δ expresses a number which satisfies a relation, 0<δ<1.